Photosensitive members such as electrophotographic or photoconductive imaging members, including photoreceptors or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers, is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems.
One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example, the charge transporting layer of a photoreceptor. This overcoat layer should satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating.
Various overcoats employing alcohol soluble polyamides have been proposed. One of the earliest ones is an overcoat comprising an alcohol soluble polyamide without any methyl methoxy groups (ELVAMIDE®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. This overcoat is described in U.S. Pat. No. 5,368,967, the entire disclosure thereof being incorporated herein by reference.
A crosslinked polyamide overcoat is known, comprising a crosslinked polyamide containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine, and referred to as LUCKAMIDE®. In order to achieve crosslinking, a polyamide polymer having N-methoxymethyl groups (LUCKAMIDE®) was employed along with a catalyst such as oxalic acid. This tough overcoat is described in U.S. Pat. No. 5,702,854, the entire disclosure thereof being incorporated herein by reference.
Disclosed in U.S. Pat. No. 5,976,744 is an electrophotographic imaging member including a supporting substrate coated with at least one photoconductive layer, and an overcoating layer. The overcoating layer includes hydroxy functionalized aromatic diamine and a hydroxy functionalized triarylamine dissolved or molecularly dispersed in a crosslinked acrylated polyamide matrix. The hydroxy functionalized triarylamine is a compound different from the polyhydroxy functionalized aromatic diamine.
Disclosed in U.S. Pat. No. 5,709,974 is an electrophotographic imaging member including a charge generating layer, a charge transport layer and an overcoating layer. The transport layer includes a charge transporting aromatic diamine molecule in a polystyrene matrix. The overcoating layer includes a hole transporting hydroxy arylamine compound having at least two hydroxy functional groups, and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups of the hydroxy arylamine compound.
Disclosed in U.S. Pat. No. 5,368,967 is an electrophotographic imaging member comprising a substrate, a charge generating layer, a charge transport layer, and an overcoat layer comprising a small molecule hole transporting arylamine having at least two hydroxy functional groups, a hydroxy or multihydroxy triphenyl methane, and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups such as the hydroxy arylamine and hydroxy or multihydroxy triphenyl methane. This overcoat layer may be fabricated using an alcohol solvent. This electrophotographic imaging member may be used in an electrophotographic imaging process. Specific materials including ELVAMIDE® polyamide and N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine and bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane are disclosed in this patent.
Disclosed in U.S. Pat. No.4,871,634 is an electrostatographic imaging member containing at least one electrophotoconductive layer. The imaging member comprises a photogenerating material and a hydroxy arylamine compound represented by a certain formula. The hydroxy arylamine compound can be used in an overcoat with the hydroxy arylamine compound bonded to a resin capable of hydrogen bonding such as a polyamide possessing alcohol solubility.
Disclosed in U.S. Pat. No. 4,457,994 is a layered photosensitive member comprising a generator layer and a transport layer containing a diamine type molecule dispersed in a polymeric binder, and an overcoat containing triphenyl methane molecules dispersed in a polymeric binder.
Disclosed in U.S. Pat. No. 5,418,107 is a process for fabricating an electrophotographic imaging member.
Phenolic overcoat compositions comprising a phenolic resin and a triarylamine hole transport molecule are known. These phenolic overcoat compositions can be cured to form a crosslinked structure.
A photoconductive imaging member having an overcoat layer that has excellent adherence to the charge transport layer is desired. Such an overcoat layer could improve the overall useful life of the photoconductive imaging member.